This invention relates to a development of the technologies described in patent publication WO 96/35457 (xe2x80x9cRAMSAYxe2x80x9d) published Dec. 28, 1995, and based on PCT/CA95/00362. The present invention relates to a fluid-handling, tapered rotor and stator sleeve assembly mounted on a rotary shaft, in which one of the sleeves is cut with opposed bidirectional helical grooves. The grooves are configured in the inventive manner described below to control thrust, improve lubrication, and/or provide bidirectional operation.
In RAMSAY, there is described a bearing and/or seal assembly for a rotary pump drive shaft, based on the use of a tapered rotor and stator sleeve arrangement. One of the sleeves is cut with a continuous helical groove along which a barrier liquid is driven, by virtue of the rotation of the rotor sleeve, and pressurized, serving to drive the barrier liquid toward the process fluid being pumped. As described, the tapered sleeve arrangement serves as a bearing and also as a liquid barrier seal. In RAMSAY, however, as far as the bearing function is concerned, only a journal bearing capability was provided. The tapered rotor sleeve was allowed to float axially in the direction of the pump drive shaft. The axial or thrust location of the rotor sleeve and shaft was balanced by some external means, such as a thrust spring or separate ball-bearing.
In order to add a thrust bearing capability to the journal bearing function of the tapered sleeve arrangement described in RAMSAY, a back-to-back, double taper sleeve arrangement was devised as described in patent publication WO 97/13084 (RAMSAY II) published Apr. 10, 1997 (based on PCT/CA96/00659). As described in RAMSAY II, each of the sleeve tapers are provided with a continuous helical groove along which a barrier liquid is conducted.
Heretofore, cylindrical journal bearing units having cooperating rotor and stator sleeves were known in which one of the sleeves was formed with a continuous helical groove or with bidirectional helical grooves along which a lubricating liquid was conducted. These bearing units utilized hydrodynamic lubrication. In the case of the continuous groove, lubricant entered at one end of the groove and was conducted to the other end which was typically closed. In the case of bidirectional grooves, the sleeve contained a left hand revolving section and a right hand revolving section which spiraled toward one another at a midpoint. The lubricant traveled along these spiral grooves until arrival at the midpoint, which was either closed or provided with a suitable opening through the lubricant exited to provide a recycled lubrication flow. Representative of such helical groove journal bearings are U.S. Pat. No. 1,923,597, U.S. Pat. No. 4,462,644, and U.S. Pat. No. 4,614,445.
The inventors have recognized that it would be advantageous to control the thrust and adjust pressure conditions at either end of the taper for a tapered seal/bearing sleeve arrangement. The inventors have also recognized that it would be advantageous to provide for a mechanism by which thrust forces across the tapered sleeve can be balanced or controlled in one direction or the other, depending on the application requirements, for a simpler approach to stabilizing thrust on the rotary shaft.
For use as a bearing and/or seal assembly mounted on a rotary shaft, such as a rotary pump drive shaft, there is provided a pair of sleeves in the form of a rotor sleeve and a stator sleeve which together define a single taper bearing surface coaxially disposed about the axis of the shaft, and a pair of oppositely directed inclined grooves each extending along at least a portion of a helical or spiral path (bidirectional grooves) through which fluid, such as liquid, is conducted to an interior zone of the grooved sleeve, such that net thrust forces across the assembly are controlled. Pursuant to the invention, the opposing grooves are specially configured respective to one another.
One or both inclined grooves of the pair of inclined grooves can be a continuous helical or spiral groove or can be one inclined groove of a plurality of spaced-apart inclined grooves.
As between the grooves, the grooves may differ in length, pitch, depth, and/or width. The opposing grooves may not coincide at a common midpoint or apex interiorly of the sleeve. The turns of the grooves may differ. The interior ends of the opposing grooves may merge into one another or be separated from one another by a circumferential groove or land and thus be discontinuous and separate. The differences as between the grooves is predesigned to yield a balanced thrust operation during rotation of the shaft, or produce a negative or positive thrust in order to offset external thrust force and maintain stability of the shaft. When simultaneously used as a barrier liquid seal assembly, the groove differences serve to control liquid pressure flow across the assembly such that process fluid is prevented from passing backward through the bearing surface interface.